During the last twenty years, the regenerated iron oxides (RIO) produced from hydrochloric acid waste liquid generated from steel pickling have been recognized as an important source of raw material for preparing products containing iron oxides such as high-grade ferrites.
One drawback of utilizing regenerated iron oxides from hydrochloric acid waste liquids generated from steel pickling is that the ferric oxides inevitably contain chloride, typically in the range of about 0.1 to 0.5% measured as grams of chloride per 100 grams of regenerated iron oxide. For the ferrite producers, the chloride ion present in the regenerated iron oxide is not only corrosive to the ferrite manufacturing installations but also injurious to the quality of the ferrite produced.
Reducing the chloride content in regenerated iron oxides by an economical procedure, without significantly changing the ferric oxide quality is believed to be one of the most critical issues for the development of regenerated iron oxides as commercially useful raw materials.
U.S. Pat. No. 1,967,235, issued Jul. 24, 1934 and assigned to K. A. Ferkel, proposes a process for production of metal oxide by contacting metal chloride vapor with water vapor to form a hydrated oxide, which is subsequently calcined to drive off water of hydration and form metal oxide. No mention was made of any method for reducing chloride level in regenerated iron oxides.
Japanese patent application number 47-39477, assigned to TDK Electronics Co, proposes heating beta-FeOOH containing 2.5% chloride at 450.degree. C. to form alpha iron oxide. No mention was made of the removal of chloride impurities from chloride-containing iron oxides.
Suganuma, et al. in 4th International Conference on Ferrites, Advances in Ceramics, Vol. 15, 81-85 (1986), reported a method for removing chloride ions from hematite powders by heating the ferric oxide in air with the addition of sulfur dioxide and/or moisture. However, sulfur oxide is a toxic gas which is unhealthy and environmentally undesirable.
Thus, there remains a need for a commercial process which will substantially reduce the chloride contents in regenerated iron oxides (RIO) at a low cost without significantly changing the quality of the iron oxides.